The figure below illustrate some important terms for a lens. The principal axis of a lens is the line joining the centers. The focal point is the point at which a beam of a parallel light, parallel to the principal axis, converges. The focal length of a lens is the distance between the center of the lens and its focal point. http://www.antonine-education.co.uk/New_items/MUS/images/ray_diag_6.gif
30.2 Image Formation by a lens
If the rays of light coming from an object actually come together to form an image it will be able to be projected on a screen so it is a real image. Real image formed by a single lense are always upright. http://www.danalee.ca/ttt/images/9/camera7.gif
If the ray can't be projected because the rays do not actually converge at the image then it is a virtual image. Virtual image will form an inverted image. 30.3 Constructing Images Through Ray Diagram.
Ray diagram can also be drawn to locate and describe the image that will be formed by a lens. The usual rays to be drawn are:
1) A ray that comes in parallel to the principal axis and goes out through the focal points.
2) A ray that comes in through the focal points and goes out parallel to the principal axis.
3) A ray that goes straight through the center of the lens.
The relationship between the focal length (f), object distance (p), and image distance (q) can also be found from the thin lens equation:
1/p + 1/q = 1/f http://kottan-labs.bgsu.edu/teaching/workshop2001/chapter2_files/image006.gif
Diverging lens, virtual image (ray diagram) http://www.physics.uq.edu.au/courses/phys1000/optics_raydiag2.png
30.4 Image Formation Summarized
Any image formed by a diverging lens will be upright and virtual. An image formed by a converging lens will be inverted and real if the object is farther than the focal length from the lens, will be upright and virtual if the object is between the lens and the focal point, and no image will be formed if the image is at the focal point.
30.5 Some Common Optical Instruments
The Camera
A camera consists of a lens and sensitive film mounted in a lighttight box. In many cameras, the lens is mounted so that it can be moves back and forth to adjust the distance between the lens and film.The lens forms a real, inverted image on the film. The image below show a camera with a single simple lens. In practice, most cameras make use of compound lenses to minimize distortion called aberrations. **http://www.physast.uga.edu/~rls/1020/ch7/fig7-04.jpg**
The Telescope
A simple telescope uses a lens to form a real image of a distance object. Telescope that use lenses are refracting telescope. Larger astronomical telescope use mirror instead of lenses.
A pair of reflecting prism is used in the terrestrial telescope, which produce an image that is right-side up. A pair of these telescope side by side, each with a pair of prisms to provide four reflecting surfaces to turn images right-side up, makes up a pair of binoculars(picture below) **http://www.odec.ca/projects/2005/dong5a0/public_html/PPrBinoc.png**
A compound microscope uses two converging lenses of short focal length, shown above. Since the image is farther from the lens than the object, it is enlarged.The instrument is called a microscope because it enlarges an already enlarged image.
The Projector
A projector is arrange by a concave mirror that reflects light from an intense source back onto a pair of condenser lenses.The condenser lenses direct the light through the silde or movie frame to a projection lens. 30.6 The Eye http://www.familyconnect.org/images/parentsite/HumanEyeDiagram.jpg
The human eye is similar to the the camera. The amount of light that enters is regulated by the iris, the colored part of the eye that surround the opening calle dthe pupil. Light enters through the transparent covering called the cornea, passes through the pupil and lens is focuseed on a layer of tissue at the back of the eye; the retina.
30.7 Some Defects in Vision http://www.hipusa.com/webmd/images/health_and_medical_reference/eye_health/understanding-vision_problems-basics-myopia-and-hyperopia.jpg Farsighted causes image to form behind the retina and nearsighted causes image to form in front of it, instead of fromoing images on the retina. These can be corrected by placing corrective lenses in front of the eyes A converging lens is needed to correct farsightedness while a diverging lens is needed to correct nearsightedness. Astigmatism of the eye is a defect that result when the cornea is curved more in one direction than other, somewhat like the side of a barrel. because of this defect, the eye does not form sharp images. The cure for this is cylindrical corrective lenses that have more curvature in one direction than in another.
30.8 Some Defects of Lenses http://www.nightlase.com.au/education/optics/Images/aberration.gif
The above picture shows aberration; defects of lens. The most common of all defects is spherical aberration. It is light passing through the edges of a speherical lens will focus at a different point than ight passing close to the center. While chromatic aberration is light of different colorswill focus at different points. Correcting spherical aberration requires that lenses be made parabolic in cross section rather than as a section a sphere. To correct chromatic aberration requires that carefully chosen pairs of lenses be used so that their chromatic aberratioon will cancel each other out.
Work Cited
Hewitt, Paul G. Conceptual Physics. Third Edition ed. Menlo Park, California: Scott Foresman Addison Wesley, 1999
30.1 Converging and Diverging Lenses
A lens is a piece of glass or other transparent material that is specially shaped to change the path of the light passing through it.
Converging lens- cause parallel light rays to all come together to a single point(called the focal point)
Diverging lens-cause parallel light rays to spread out as if they came form a focal point on the other side of the lens.
The figure below illustrate some important terms for a lens. The principal axis of a lens is the line joining the centers. The focal point is the point at which a beam of a parallel light, parallel to the principal axis, converges. The focal length of a lens is the distance between the center of the lens and its focal point.
30.2 Image Formation by a lens
If the rays of light coming from an object actually come together to form an image it will be able to be projected on a screen so it is a real image. Real image formed by a single lense are always upright.
http://www.danalee.ca/ttt/images/9/camera7.gif
If the ray can't be projected because the rays do not actually converge at the image then it is a virtual image. Virtual image will form an inverted image.
30.3 Constructing Images Through Ray Diagram.
Ray diagram can also be drawn to locate and describe the image that will be formed by a lens. The usual rays to be drawn are:
1) A ray that comes in parallel to the principal axis and goes out through the focal points.
2) A ray that comes in through the focal points and goes out parallel to the principal axis.
3) A ray that goes straight through the center of the lens.
The relationship between the focal length (f), object distance (p), and image distance (q) can also be found from the thin lens equation:
1/p + 1/q = 1/f
Diverging lens, virtual image (ray diagram)
30.4 Image Formation Summarized
Any image formed by a diverging lens will be upright and virtual. An image formed by a converging lens will be inverted and real if the object is farther than the focal length from the lens, will be upright and virtual if the object is between the lens and the focal point, and no image will be formed if the image is at the focal point.
30.5 Some Common Optical Instruments
The Camera
A camera consists of a lens and sensitive film mounted in a lighttight box. In many cameras, the lens is mounted so that it can be moves back and forth to adjust the distance between the lens and film.The lens forms a real, inverted image on the film. The image below show a camera with a single simple lens. In practice, most cameras make use of compound lenses to minimize distortion called aberrations.
**http://www.physast.uga.edu/~rls/1020/ch7/fig7-04.jpg**
The Telescope
A simple telescope uses a lens to form a real image of a distance object. Telescope that use lenses are refracting telescope. Larger astronomical telescope use mirror instead of lenses.
A pair of reflecting prism is used in the terrestrial telescope, which produce an image that is right-side up. A pair of these telescope side by side, each with a pair of prisms to provide four reflecting surfaces to turn images right-side up, makes up a pair of binoculars(picture below)
The Compound Microscope
A compound microscope uses two converging lenses of short focal length, shown above. Since the image is farther from the lens than the object, it is enlarged.The instrument is called a microscope because it enlarges an already enlarged image.
The Projector
A projector is arrange by a concave mirror that reflects light from an intense source back onto a pair of condenser lenses.The condenser lenses direct the light through the silde or movie frame to a projection lens.
30.6 The Eye
The human eye is similar to the the camera. The amount of light that enters is regulated by the iris, the colored part of the eye that surround the opening calle dthe pupil. Light enters through the transparent covering called the cornea, passes through the pupil and lens is focuseed on a layer of tissue at the back of the eye; the retina.
30.7 Some Defects in Vision
Farsighted causes image to form behind the retina and nearsighted causes image to form in front of it, instead of fromoing images on the retina. These can be corrected by placing corrective lenses in front of the eyes A converging lens is needed to correct farsightedness while a diverging lens is needed to correct nearsightedness.
Astigmatism of the eye is a defect that result when the cornea is curved more in one direction than other, somewhat like the side of a barrel. because of this defect, the eye does not form sharp images. The cure for this is cylindrical corrective lenses that have more curvature in one direction than in another.
30.8 Some Defects of Lenses
The above picture shows aberration; defects of lens. The most common of all defects is spherical aberration. It is light passing through the edges of a speherical lens will focus at a different point than ight passing close to the center. While chromatic aberration is light of different colorswill focus at different points. Correcting spherical aberration requires that lenses be made parabolic in cross section rather than as a section a sphere. To correct chromatic aberration requires that carefully chosen pairs of lenses be used so that their chromatic aberratioon will cancel each other out.
Work Cited
Hewitt, Paul G. Conceptual Physics. Third Edition ed. Menlo Park, California: Scott Foresman Addison Wesley, 1999